Antonyms for the phrase "is unable to decide" include "decisive," "resolute," "determined," and "unwavering." These words indicate a sense of certainty and firmness, indicating that the person in question is confident and assertive in making decisions. Other potential antonyms could include "confident," "certain," "uninhibited," "unflappable," and "resilient." All of these words suggest a level of self-assurance and assertiveness, allowing the individual to make decisions with ease and conviction. By contrast, someone who is unable to decide may be described as "indecisive," "hesitant," "uncertain," or "ambivalent." Such individuals may struggle to make choices or may frequently change their minds.